I have read so many conflicting reports of the damage compressor surge can do. some folk saying wear and tear on turbo\'s causing end-float etc.
Other folk saying it causes no problems whatsoever i.e your turbo\'s are under far more stress just spooling up everytime you put you foot down so the stress is next to nothing. Nothing but an excellent bit of marketing etc etc
Many tuners use/don\'t use them for many different reasons.
Is running without a bov for short periods of time (as in all summer) really gonna cause any problems????
I would say depends more on the turbo you are runnning. Big turbo\'s seem to take compressor surge quite well. Small turbo\'s not so well. The only real thing you can go on is asking people how long that specific turbo has lasted other people.
Has allot to do with what turbo you are running/Power your running/How much abuse you give it and things like that. Don\'t forget the Most Boost your giving it the more Violent the effects.
I had a T04R that was put together by Innovative in the US, i ran that for 2-3 years with no bov as an ever day car, after that time i could honestly say there was little wrong with it.
On the other hand i know people that have had issues, but at the end of the day its an educated risk, that said if i was running big HP i would proberly not think twice about fitting one.
So from what your saying on a standard twin set-up running standard boost the effects would be minimal right?.
But with a big single running plenty o boost a bov is advised
Correct?
think of the turbo as a propellor and u put air through the front and spin the blades then put the same amount of air thru the back at the same time as cutting the air at the front..quite a shock to the system when u are talking abut the rpm of the blades
bov are a safety device first and foremost..forget the sound all road going turbos have either a bov or relief valve for one reason longevity of the turbo
if u want ur turbo to last fit a bov if u want to take a chance then dont its that simple
forget the comments about ive not had one for this and that each person makes their own choice sometimes without really knowing what the vave does
and of course the rally cars dont run them thats because they dont wory as the team strip and rebuid the parts regular ie after every race and dont have to pay for the things
Big turbos with lots of boost even with a dv you stall get compressor surge because it can\'t expell enough boost quick enough.
Any way compressor stall on stock twins probably causes more damage than say a t04r at 1bar with no dv. It\'s more to do with the bearings of the turbo.
Quote from: neil_jdmrSo from what your saying on a standard twin set-up running standard boost the effects would be minimal right?.
TBH i\'ve never seen it done with Twins.
Quote from: TimmyIt\'s more to do with the bearings of the turbo.
Yup, I have always been lead to believe its the bearings. Stock turbos dont have a 360deg bearing. You
could run without a bov but I wouldn\'t want to do so myself.
so no-one with standard twins has ever ran without a bov, I honestly cannot see why whether the compressor blades run forwards or backwards would decrease the life of the bearings. Surely like all bearings they are designed to run both ways and only the blades are slanted to deliver air in any one direction.
My other point would be i understand that holding pressure in a system would be harmful but even without a bov the air would pass through the blades and out of the exhaust hence no build up in pressure.
Has anyone any real experience of damage that not having a bov causes or the usual horror stories just being repeated?
Before anyone jumps in to give me an ear bashing i am only throwing in these questions as it helps me learn more. i am not planning on blanking my bov off personally but am keen to know the TRUE affects this has. From my experience in industry the only reason bov/prv are used is to release when a set pressure is exceeeded and has nothing to do with compressor life preservation.
Again iam only asking questions and not looking for a lashing
Quote from: Ricco_04Yup, I have always been lead to believe its the bearings. Stock turbos dont have a 360deg bearing. You could run without a bov but I wouldn\'t want to do so myself.
Actually its more to do with Shaft failure (Imagen the amount of Exhaust gases does not change but on the other side of the turbo the Throttles are now shut,simply the pressure will build on the colds side until both sides are the same then the compressor stalls, all this happens in hundredths of second) the bearings will let go if you run higher boost levels, 360\'s help with that, the surge is renown for snapping shafts. Thats why the bigger turbo\'s handle it better (T series turbo\'s hard thicker shafts which made them stronger but also heavier)
If that made sense...
the dump valve has nothing to do with releasing pressure when it reaches a certain point
the wastegate controls the pressure and stops u boosting to silly levels in excess of your mapping
the bov will stay shut(failing a fault)until u lift off pressure by lifting the pedal
your engine will explode long before the d/valve will release pressure it is a simple device on boost the valve is forced shut and will stay shut until u lift off the pressure at which point the valve will vent the air either to atmo or recirc thru the intake
Quote from: neil_jdmrHas anyone any real experience of damage that not having a bov causes or the usual horror stories just being repeated?
Well not me personally but i\'ve seen the damaged caused on 5 turbo\'s etc when running high boost with no BOV. I can tell you 100% it can be catastrophic damage (the main one is Shaft failure or bent shafts but i\'ve seen bent Fins on Wheels and even blades missing dues to surge or so i was told by the Turbo people) tbh i would not be at all suprised if the bearing may need changing after a Shaft failure????
mazda didn\'t fit a BOV to the stock car for no reason, everything was put through R&D
Quote from: rx7veilsidethe dump valve has nothing to do with releasing pressure when it reaches a certain point
the wastegate controls the pressure and stops u boosting to silly levels in excess of your mapping
the bov will stay shut(failing a fault)until u lift off pressure by lifting the pedal
your engine will explode long before the d/valve will release pressure it is a simple device on boost the valve is forced shut and will stay shut until u lift off the pressure at which point the valve will vent the air either to atmo or recirc thru the intake
Yes mate
I understand that but the bov is there to release the pressure left in your system once you lift off and if it isnt released to atmos/re-circ it is released back through the blades and out the exhaust.
I think im getting it now,
So because once ive lifted off milliseconds before the bov opens the turbo is still spinning ( over spinning effectively) and the pressure build up between the turbo and the still closed bov would stall the compressor until it forces it backwards hence forcing it one way then the other. Is it the fact that the pressure changing the direction of the compressor that causes problems???
If so surely when driving off boost before the compressor gets spinning the exhaust is drawing air turning the compressor backward anyway???
there is a big thread on ausrotary with Pros and Cons. Been discussed many times on here.
On standard twins keep the valves as MAzda intended as the turbos and shafts on twins are small, if you run a big shaft single turbo no point, Id rather keep the performance benefit of running without bov, plus I have seen no damage on my turbo or others that run without on big singles.
If ya scared of damage then run a BOV
Quote from: neil_jdmrSo because once ive lifted off milliseconds before the bov opens the turbo is still spinning ( over spinning effectively) and the pressure build up between the turbo and the still closed bov would stall the compressor until it forces it backwards hence forcing it one way then the other.?
The compressor wheel does NOT STOP SPINNING or Stall.
Exhaust gas is still turning the Turbine BLade!! it will not rotate in the other direction!
The other man use of the recirc valves was to do with emissions
That\'ll do me
Thanks gent\'s
Quote from: BlitzBoyThe compressor wheel does NOT STOP SPINNING or Stall.
Would you say it puts more load on the shaft between the Hot and cold side? i.e. the extra pressure in the Inlet tract physically trying to stop the the Compressor wheel or pushing air back past the wheel while its still spinning causing the Chirp noise.
I think i ment to say it starts to stall (as you say it doesn\'t actually stop) but it does slow quicker due to the extra Force created by the pressure in the Compressor/inlet.
Quote from: BlitzBoyThe compressor wheel does NOT STOP SPINNING or Stall.
Exhaust gas is still turning the Turbine BLade!! it will not rotate in the other direction!
The other man use of the recirc valves was to do with emissions
Hi Mark,
I beg to differ,if the throttle is shut then there is no longer any exhaust gas driving the turbine,then you do indeed get air rushing back over the compressor which can slow it down,it makes a chirrupping noise and it tries to do this in a cycling fashion.
You are right that certain setups are fine without,but it does depend on the type of turbo,and also it\'s end use.
Also if dump valves were not needed then manufacturesrs would not put them onto production cars as it would save them money,and we all know that if they think a corner can be cut then they will cut it.
Regards
Carl
sure there is some type of load on the shaft but its negliable on a big single, it wont see anywhere as much as the engine sees, eg say you running 10 psi you wont get 10 psi passing back over the blades probably 2-4psi, you can read all the different theories on that Ausrotary thread.
Quote from: BlitzBoysure there is some type of load on the shaft but its negliable on a big single, it wont see anywhere as much as the engine sees, eg say you running 10 psi you wont get 10 psi passing back over the blades probably 2-4psi, you can read all the different theories on that Ausrotary thread.
Quite right.
Hows your new bridgeport going?
Regards
Carl
I was just thinking what carl said, with no throttle, there\'s no exhaust gasses and hence no boost per se.
But tell me this, while we\'re on the subject, if I\'m gently accellerating, and making zero pressure on my boost gauge, then the turbos are still "doing work"? Just nto made it to +ve pressure right?
So to cool down you really need to be very gentle ont he throttle?
I think we are talking in msseconds here lol once you snap the throttle shut im sure there is still some exhaust gas and heat still turning the turbine wheel, and im sure the wheel is still turning at still some rpm, you see what we need is a high speed camera in there to tell us lol
Turbos are always working when gently cruising
Quote from: RemarkLimaI was just thinking what carl said, with no throttle, there\'s no exhaust gasses and hence no boost per se.
in a nut shell the amount of time from the 10psi (e.g.) passing through the throttles going round the Rotor Firing and out the exhaust is the time the Turbo will see Surge.
Out of intrest, if you rev your engine with the outlet of turbo blocked off how much pressure will you see in the Comp housing????? will it be 10psi if the waste gate is set to 10Psi? i guess it all depends on how much of a damper you have.
Quote from: RemarkLimaSo to cool down you really need to be very gentle ont he throttle?
Ideally cool down should see no + boost.
Look at it this way the throttle closes and the air hits the closed throttle and bounces back through the system normaly finding it\'s way though a dv. In this case it has no where to go but back through the turbo. On hitting the turbine which is spining still it pushes against the fins in the opposiet way to usual slowing it down. Theoreticaly this puts a twisting force on the shaft also cud bend the fins of the shaft very bad for ceramic turbines as they will just shatter. Also the forces probably push the bearings in an odd way maybe causing a metal on metal contact for 1/10000th of a second.
In other words only bother if you have a large turbo as the shaft will be thicker and also the finns.
The bearing damage will probably take a long time to become a problem so even on a big turbo you will reduce the life of it. You could just buy a hks ssqv the old tyoe thats adjustable and adjust it nice and stiff and your get a little bit of stall along with a dump. Probably just stall at low boost levels.
no way would compressed air bend the fins in the boost levels we are talking about, hell top end turbo drag cars that run 40 plus psi dont run BOVs and they dont break fins or shafts
Quote from: BlitzBoyno way would compressed air bend the fins in the boost levels we are talking about, hell top end turbo drag cars that run 40 plus psi dont run BOVs and they dont break fins or shafts
They don\'t shut the throttle though the run and between gear changes either,so it won\'t be a problem for them anyway,that is why they don\'t run them.
The compressor does slow down on clutched manual shifts,so a slight amount of time maybe can be gained by keeping the turbo rotating by using a dump valve,rather than it having to respool even slightly after each manual gear change.
Regards
Carl
I beg to differ I believe you lose time with a dump valve as you have to repressurize the intercooler pipes so you slower building boost.
Thats why WRC cars run without BOVs as they do many many gear changes per rally time is lost building boost with a DUMP valve.
I done back to back drag runs when I run the the T04R turbo and I disabled the bov i had at the the time and my quarter miles were better
Quote from: BlitzBoyno way would compressed air bend the fins in the boost levels we are talking about, hell top end turbo drag cars that run 40 plus psi dont run BOVs and they dont break fins or shafts
Ok, what other reason is there for blades to come off a Garrett turbo?? i was only told it was Due to Surge.
We aint talking top end best you can buy turbo\'s, lets face it most of the T series are x truck?
If you run a recirculating dump valve then you don\'t lose any boost at all.
Regards
Carl
Luv to see to see these pics of these big single turbos with broken blades due to surge, the only ones i have seen broken is due to debris getting into the compressor housing.
Anyway im not really arguing there is evidence for and against BOvs. I run without because of performance and have had no ill effects in two years of hard driving on my turbo, plus speaking to guys down under who are into drag with similar sort of setups to me also run without bovs coz of performance
No because a wrc has this little thing called anti lag and it\'s alot more than just a throttle kicker. So the turbo produces boost without any throttle caused by an injector in the exhaust manifold.
I think you\'ll find if you look at the boost gauge with or without a dv the system looses all boost pressure.
In fact i don\'t think there are any performance gains from not running a dv at all.
As carl said full throttle changes when you do a drag run so maybe there\'s room for improvement on you 11.39
Come on Mark,tell us about your new bridgeport.
Regards
Carl
Quote from: GrizzlyOk, what other reason is there for blades to come off a Garrett turbo?? i was only told it was Due to Surge.
We aint talking top end best you can buy turbo\'s, lets face it most of the T series are x truck?
exactly.
who knows the history of the turbo plus a lot of turbos on the market are old truck technology, not designed for loads of boost pressure.
If a turbo is run with a filter so no debris can get in the fins can only be caused by 2 other things imo. Bearing failure cause shaft play so the fins touch the housing. Obviously on stip down you\'d have lots of shaft play or compressor surge.
Mark,
here is a couple of pics of the second fastest rotary in the world up the strip,you are right,they are not running a dump valve,they are actually running two!
Regards
Carl
has that thing got 3 turbos?
Quote from: Timmyhas that thing got 3 turbos?
Yes it has.
Regards
Carl
Even Abel Ibarra has on his car which is the fastest rotary in the world.
Look at this vid where you can clearly see it/them.http://videos.streetfire.net/video/f1e022e3-bcb6-4843-91a0-99b001670330.htm
Regards
Carl
lol for every picture you post of a drag car with a BOV I can post several pics of drag cars without BOVs Carl, plus I have intercooler and more length of tubes to pressurise rather then the methonal cars without coolers, I am more concerned with the class of car that im up against, and with my setup my car is quicker without a BOV in this case
turbine is constantly spinning whilst the engine is running whether at WOT, cruise, foot off the gas etc
bare in mind that the expansion of the thermal heat has more effect on the turbine spinning then flow of the gasses, hence why some people use turbo beanies to keep the heat in the rear turbine of the housing.
As I said there are Pros and cons to Dump valves. On my setup with an intercooler and long pipes is beneficial not to have a dump valve,
There are Drag cars they dont run them and some that do, remember these guys test all the time and would either add or take them off if it makes their cars quicker, some find they are quicker without them.
Anyways we can debate this till the cows come home, im going to bed lol
Quote from: CarlMark,
here is a couple of pics of the second fastest rotary in the world up the strip,you are right,they are not running a dump valve,they are actually running two!
Regards
Carl
I\'m also loving the lack of Intercooler! But then they make up for it with the massive front mount oil cooler! Suppose not worth the extra weight -not exactly like it be doin big distances.
What size you recon the three turbo\'s are? Bet that was an interesting choice as to what to go for.
As an aside - there are some production FI cars that are not fitted with recirc/BOV valves :nod: S13 200sx for one... ;)
Quote from: rotariI\'m also loving the lack of Intercooler! But then they make up for it with the massive front mount oil cooler! Suppose not worth the extra weight -not exactly like it be doin big distances.
What size you recon the three turbo\'s are? Bet that was an interesting choice as to what to go for.
I don\'t know what turbo\'s they are,maybe something like gt35r\'s,but the reason for no intercooler is they are running methanol for fuel which in itself has a very dramatic cooling effect.
Regards
Carl
Quote from: CarlIf you run a recirculating dump valve then you don\'t lose any boost at all.
Regards
Carl
by this do you mean recric it into the intake as on the stock set up? surely the only way you could maintain boost would be if the air filter provided sufficent restriction to ensure the pressuried air went to the turbo inlet rather than to atmosphere through the filter. if this was true then the turbo would have to overcome a large presure difference to get ari into the engine during normal operation- hindering performance. this isn\'t the case as air filters are designed to provide as little restriction as possible, and so the pressure is going to dissipate very quickly.
on the other hand whilst the preasure from the dump/recirc valve will reduce to atmospheric rapidly, the temperature diffusion of the hot air put into the inlet would be much slower- so when the turbo did spool up again after gear change or whatever, it would be drawing in hot air pretty much straight from the turbo outlet. so from a preformance point of view, it would be slightly better to have the dump valve going to atmosphere, as in effect that is all a recirc valve does anyway, and it eliminates a source of hot air into the intake?
Obviously i could be wrong on this and await my argument to be shot to pieces.....
marco
Carl Recirc valves still lose you boost on the stock setup, the other main use of recirc valves was to eliminate noise of the dumped air by feeding it back into the Air filter Air box on the stock setup, therefore eliminating the Tsccchhh noise as you would get from normal DVs, Mazda couldnt release a car which make weird and wonderful noises of strange plumbing lol, thats why Manufacturers sell cars with recirc valves and not atmos DV on turbo cars, they are a noise surpressant device (recirc valves) as well
On a car with an AFM rather than a MAF sensor, a recirculating valve helps the car run a lot better than a BOV as well. Obviously, this isn\'t relevant to most on here, but with a MAFif air is dumped out of the inlet tract after the MAF has metered it, then the car is supplying fuel for air that isn\'t there - hence momentary richness. This can make the car stumble between gear changes, as well as damping unburnt fuel down the exhaust.
My S14a ran soo much smoother with the stock recirc valve than it did with no valve at all, or with a vent to air valve.
On my FD I\'m going to be running an HKS SSQV in VTA mode. For two main reasosn: 1, it was free, and 2, it neatens up some of the pipework in the bay.
Quote from: GrizzlyActually its more to do with Shaft failure (Imagen the amount of Exhaust gases does not change but on the other side of the turbo the Throttles are now shut,simply the pressure will build on the colds side until both sides are the same then the compressor stalls, all this happens in hundredths of second) the bearings will let go if you run higher boost levels, 360\'s help with that, the surge is renown for snapping shafts. Thats why the bigger turbo\'s handle it better (T series turbo\'s hard thicker shafts which made them stronger but also heavier)
If that made sense...
Yes makes sence - understand better now! :Thumbs-up
Quote from: CarlAlso if dump valves were not needed then manufacturesrs would not put them onto production cars as it would save them money,and we all know that if they think a corner can be cut then they will cut it.
Regards
Carl
Could be wrong (again :o ) but I thought the main reason they used recirc valves was so they could get rid of the compressor surge noise, as in having a quieter/more refined car?
Quote from: Ricco_04Yes makes sence - understand better now! :Thumbs-up
Could be wrong (again :o ) but I thought the main reason they used recirc valves was so they could get rid of the compressor surge noise, as in having a quieter/more refined car?
you are correct , exactly my point on recirc valves I made earlier, haha this debate will live forever lol
Quote from: BlitzBoyCarl Recirc valves still lose you boost on the stock setup, the other main use of recirc valves was to eliminate noise of the dumped air by feeding it back into the Air filter Air box on the stock setup, therefore eliminating the Tsccchhh noise as you would get from normal DVs, Mazda couldnt release a car which make weird and wonderful noises of strange plumbing lol, thats why Manufacturers sell cars with recirc valves and not atmos DV on turbo cars, they are a noise surpressant device (recirc valves) as well
You are quite right Mark,my bad,
I did get this all wrong.
I was getting muddled up with the setup that is often used on a supercharger where it is driven by the engine\'s rotation.
Regards
Carl
vented to air dump valves are also an issue with emmissions. due to possible oil carry over from the turbo bearings and then venting to atmosphere.
So there is another reason why they are used on OEM turbo applications.
I think the main issue with vent to air valves is that the charge air, which will have been metered in a stock system will have a measure of fuel added per whatever tables the ECU is working from.
When you shut the throttles and the BOV let\'s the air out, the fuel is still in the system, but the air isn\'t there anymore, so you get a pop/flame and emissions will be richer as a result. The recirc keeps the air in the system because it feeds back into the inlet, but it\'s recirculated after the Air flow meter.
Obviously most of you single tubby guys have dispensed with the MAF / AFM anyway so it\'s not relevant
Quote from: ProfI think the main issue with vent to air valves is that the charge air, which will have been metered in a stock system will have a measure of fuel added per whatever tables the ECU is working from.
When you shut the throttles and the BOV let\'s the air out, the fuel is still in the system, but the air isn\'t there anymore, so you get a pop/flame and emissions will be richer as a result. The recirc keeps the air in the system because it feeds back into the inlet, but it\'s recirculated after the Air flow meter.
Obviously most of you single tubby guys have dispensed with the MAF / AFM anyway so it\'s not relevant
I thought this was only the case with a AFM, as it\'s been measured how much air has passed, while the MAP sensors are after the throttle body hence unaffected by this (hence, Manifold Absolute Pressure).
But I know this was a huge issure on MR2 Tubbies as they had a AFM, so you\'d dump this metered ait to atmos, it\'s spike to being very rich, the lamda sensor would report this and the ECU would wet itself and cut a load of fuel just as you\'re giving it some beans and you\'d get very lean and a load of detonation :(
Sorry, just reread and saw you\'re saying a MAF sensor, when I\'m sure the FD runs a MAP sensor.
prof, thats the thing, recircing back into the inlet would only work if the air could not escape through the airfilter. as it is you have around 1bar differential pressure across a very low resistance foam/mesh filter, and so it is going to equalize very quickly. the net result is that the air from the BOV is going to return to atmospheric pressure by exhausting the excess out through the filter- a net out flow of air. the only way to recirc would be to have a one way valve between the airfilter and inlet tract.
Quote from: ProfI think the main issue with vent to air valves is that the charge air, which will have been metered in a stock system will have a measure of fuel added per whatever tables the ECU is working from.
When you shut the throttles and the BOV let\'s the air out, the fuel is still in the system, but the air isn\'t there anymore, so you get a pop/flame and emissions will be richer as a result. The recirc keeps the air in the system because it feeds back into the inlet, but it\'s recirculated after the Air flow meter.
Obviously most of you single tubby guys have dispensed with the MAF / AFM anyway so it\'s not relevant
Prof on a FD a MAF/AFM sensor is NOT used (the FC is different), a MAP sensor with an air signal of the Plenum is used. The recirc valves used on the FD is mainly used as a noise suppressant.
edit oops someone beat me to it lol
Quote from: BlitzBoyProf on a FD a MAF/AFM sensor is NOT used (the FC is different), a MAP sensor with an air signal of the Plenum is used. The recirc valves used on the FD is mainly used as a noise suppressant.
edit oops someone beat me to it lol
I keep forgetting that... :rolleyes: So apart from the noise issue, there really is no difference going for recirc or atmospheric, apart from possibly recircing air warmed by the compressor and turbo back into the system with a recirc, where a BOV would vent it off into the engine bay (in most cases - to be sucked back in through the air filter, as most folk, myself included do not provide a direct cold air feed or shroud the filter in a cold air box :Laugh ) - so no difference then...
all depends if you prefer dump valve noises or not or real mans noise of compressor surge ala Rally style lol, some big single turbos have anti-surge compressor housings which get rid some of the surge noise